The overall objective of this proposal is to better understand the pathophysiology of Type 2 diabetes mellitus (T2DM). Increased cytoplasmic Ca2+ concentration ([Ca2+]c) in pancreatic ?- cells stimulates insulin secretion. Much is known about K+ and voltage-gated Ca2+ currents that contribute to Ca2+-dependent signal transduction and insulin secretion; relatively little is known about other Ca2+ channels that regulate ?-cell Ca2+ signaling dynamics. Our published work suggests that store-operated cation (SOC) channels regulate glucose-stimulated changes in ?-cell [Ca2+]c and insulin secretion. Preliminary evidence also suggests that store-operated Ca2+ entry (SOCE) is abnormal in islets of Langerhans isolated from a mouse model of T2DM. Knowledge about SOC channels (ISOC) in ?-cells is limited: we neither know their molecular identity, nor have complete understanding of the biophysical properties or mechanisms that control ISOC activation. We will focus on defining the molecular basis of SOCE in mouse and human ?-cells. We will use a novel and innovative combination of experimental approaches that includes biosensor imaging technology, patch-clamp electrophysiology, molecular engineering with RNA interference (RNAi) and conditional gene deletion in transgenic mice to: [A] define the molecular basis and biophysical properties of ISOC in ?-cells, [B] determine the molecular mechanisms that activate SOCE, [C] define the roles of SOCE in ?-cell function, and [D] determine whether defects in SOCE contribute to ?-cell defects associated with T2DM. Our proposed studies will provide exciting new information essential for advancing understanding of stimulus-secretion coupling mechanisms in ?-cells, novel insights into ?-cell failure in T2DM, and suggest new molecular targets for treatment of T2DM.